The technique of intravenous, intra-arterial or intra-lymphatic vessel therapy by the invasion process, either for therapeutic or diagnostic purposes, is well known and standard medical procedure. A puncture into the vessel site is required to permit a needle, syringe or catheter to be inserted, thereby permitting the infusion of a fluid. When the inserted needle, syringe or catheter remains fixed in the vein, artery or lymphatic vessel, fluid entering the vessel mixes with the flow of blood and travels the path designated by the particular vessel to its tributaries. If the needle or catheter, through any inadvertent means, punctures the vessel, an egress of fluid into the surrounding tissues ensues. This egress can be caused by a number of means, including: direct puncture, wearing; degradation of the vessel wall; general fragility of the vessel wall; or chemical destruction of the wall. When this occurs, the infusing fluid is directed into the surrounding tissue cells. Such misdirection of infusion fluid during the course of therapy or diagnostic procedure is considered an "infiltration". The result can be an irritation, swelling, or inflammation of the surrounding tissues as well as the development of clots therein, all in combination or singularly developing, depending upon the amount of invasive fluid and the type of material being infused. It will be appreciated that infiltration is a painful situation and dangerous to the welfare of the patient under treatment.
Prior art infiltration detection devices depend on mechanical or electrical sensors of back pressure in the fluid delivery system. Such sensors are necessarily complex and expensive. Moreover, for safety's sake, such sensors have to be adjusted to respond in a highly sensitive manner to any back pressure condition; as a consequence, a false indication is often developed due to such occurrences as a temporary restriction or bending in the supply tube. Back pressure detection by the sensors results in an alarm sounding, which, particularly in the case of a false alarm, is an unnecessarily frightening condition for the patient.
It is therefore an object of the present invention to provide a simple and inexpensive method and apparatus for sensing infiltration whereby the aforesaid disadvantages of the prior art are eliminated.
As will be described in greater detail below, the present invention utilizes the known capability of liquid crystal material, when disposed flush against the skin, to indicate sub-cutaneous temperature changes. For example, U.S. Pat. No. 3,998,210 to Nosari (which patent is incorporated herein by reference) describes a liquid crystal strip secured to a patient's skin in order to permit visual location of a vein for a fluid infusion procedure. The films described therein, as well as the color range and chemicals described, are applicable to the present invention, the difference being that in the present invention the particular films defined by the Nosari patent are utilized for a new and unobvious purpose.